1. Field of the Invention
The present invention relates to a drive force transmission which transmits a full rotation and transforms the full rotation into a half turn. More specifically, the invention relates to a drive force transmission in a sewing machine, for transmitting a drive force from a rotary shaft, such as an arm shaft (spindle), which fully turns in synchronism with a motor, to a shuttle section which moves in a swing or in a half turn in alternative directions.
2. Discussion of the Related Art
A conventional sewing machine is provided with a drive force transmission which transmits a drive force from the arm shaft of full turn to a shuttle section to repeat a half turn motion as the result of a swing motion caused by the drive force. A half turn transmission mechanism as shown in FIGS. 9 and 10 has been known as the drive force transmission.
In the example of FIG. 9, reference numeral 81 designates an arm shaft; 82, a coupling rod; 83, a large pendulum; 84, an output shaft (oscillating shaft); and 85, a shuttle section. As shown, a pulley 81a and a crank 81b are attached to the arm shaft 81. The crank 81b is coupled with the upper end of the coupling rod 82. The lower end of the coupling rod 82 is coupled with a lever 83a of the large pendulum 83.
A gear 83b of the large pendulum 83 is in mesh with a gear 84a of the oscillating shaft 84. The shuttle section 85 is mounted on the end of the oscillating shaft 84. The shuttle section 85 includes a shuttle 85a, a half-turn hook press 85b, and the like. As already known, the shuttle section contains therein a bobbin case, a bobbin, a half-turn hook, and a driver.
In the example of FIG. 10, reference numeral 91 designates an arm shaft; 92, a coupling rod; 93, a large pendulum; 94, an output shaft (oscillating shaft A); 95, a shuttle section; 96, an additional oscillating shaft; 97, an output shaft (oscillating shaft); 98, a shuttle section. The upper end of the coupling rod 92 is coupled with a crank 91b of the arm shaft 91. The lower end of the coupling rod 92 is coupled with a lever 93a of the large pendulum 93. A gear 94a of the oscillating shaft 94 is in mesh with a gear 93b of the large pendulum 93. The shuttle section 95 meshes with the end of the oscillating shaft 94.
A gear 96a of the additional oscillating shaft 96 meshes with the gear 93b of the large pendulum 93. A gear 97a of the oscillating shaft 97 is in mesh with a gear 96b arranged at the end of the additional oscillating shaft 96. A shuttle section 98 is mounted on the end of the oscillating shaft 97. Accordingly, the shuttle section 98 is disposed in opposition to the shuttle section 95. Thus, two needles are used in the sewing machine described above.
The conventional drive force transmission for the shuttle section suffers from the following problems.
(1) In the example of FIG. 9, in a case where the oscillating shaft 84 used is long, the shaft is deflected, and the half-turn thereof causes a deflection or a twist between the gear 84a and the shuttle section 85. The deflection and twist can be deterred by increasing the thickness of the oscillating shaft 84. In this case, the weight of the drive force transmission including such a thick oscillating shaft 84 is correspondingly increased. Further, a large inertia is generated in the oscillating shaft when it repeats a half turn motion, thereby making gear sound noisy and vibration unnegligent. PA0 (2) In a case as shown in FIG. 9 where a drive force is transmitted through a following route: the arm shaft (full turn).fwdarw.large pendulum (swing).fwdarw.oscillating shaft (half turn), and the shaft for the half turn is used as the output shaft, the load (inertia, etc.) of the gear, gear sound, and twist of the oscillating shaft are small unless the output shaft is long. In a case as shown in FIG. 10 where a drive force is transmitted through a following route: the arm shaft (full turn).fwdarw.large pendulum (swing).fwdarw.additional oscillating shaft (half turn).fwdarw.gear 96b (half turn).fwdarw.gear 97a (half turn), that is, the half turn is transmitted from the shaft of half turn (additional oscillating shaft) to another shaft 97 (oscillating shaft), a mass of the half turn transmission mechanism is increased, and the inertia by the half turn becomes large. Further, since the long shaft, or the additional oscillating shaft, is used, it affects an influence on the twist of the additional oscillating shaft. As a result, the gear sound and vibration are increased.
As in the example of FIG. 10, when the gear 93b of the large pendulum 93 is combined with a long gear like the gear 96a of the additional oscillating shaft 96, it may be slid in the axial direction. When the long gear is used, the weight thereof is increased and the inertia caused by the half turn is increased.
In an example of FIG. 11, a connection member 101, such as a sleeve 99 or a coupling 100 as shown in FIG. 12(a) or 12(b), is used. It may be slid in the axial direction. This case also suffers from the increase of the weight and inertia.